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Electrical and Contractile Activity of the Heart
Overview
24
Anatomy
Undergraduate 1
02/28/2013

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Cards

Term
What is the ectopic focus?
Definition
The region of spontaneous firing other than the SA node
Term
If the SA node is damaged, what may take over governance of heart rhythm?
Definition
The ectopic focus
Term
Nodal rhythm
Definition
Ectopic focus in AV node
Term
Will a nodal rhythm (ectopic focus in the AV node) raise or slow heartbeat?
Definition
Slow - to about 40-50bpm
Term
What is the difference between the membrane potential of skeletal muscles and those of the SA node?
Definition
They dont have a stable resting membrane potential
Term
Pacemaker potential
Definition
The gradual depolarisation of the resting membrane potential of cells of the the SA node
Term
At what voltage the resting membrane potential of the SA node begin at?
Definition
-60mV
Term
What is the threshold for the membrane potential of the SA node at which voltage-regulated fast calcium-sodium channels open
Definition
-40mV
Term
What happens when the membrane potential of the SA node reaches its threshold of -40mV?
Definition
Voltage-regulated fast calcium-sodium channels open, and both Ca2+ and Na+ flow in from ECF - makes rising phase (polarisation) of action potential
Term
What happens at the peak of the membrane potential of the SA node?
Definition
K+ channels open and K+ leaves cell
Term
What happens to the membrane potential of the SA node as K+ leaves the cell?
Definition
It enters a repolarising phase
Term
Each depolarisation of SA node sets off what?
Definition
One heartbeat
Term
Why do signals slow in the AV node?
Definition
Cardiocytes are thinner and fewer gap junctions
Term
Do electrical signals quicken or slow down in the AV node?
Definition
Slow down
Term
Why is it beneficial that signals in the AV node are slowed down?
Definition
It allows ventricles time to fill with blood before they begin to contract
Term
Signals reach where in the heart first, before they reach the rest of the myocardium?
Definition
Papillary muscles
Term
Ventricle systole begins where?
Definition
At the apex, then travels upwards
Term
Ventricular cardiocytes are arranged in what formation?
Definition
Spiral - so ventricles twist slightly as they contract
Term
Why do the ventricles twist slightly as they contract?
Definition
The ventricular cardiocytes are arranged in a spiral formation
Term
What is the difference between the membrane potential of cardiocytes and that of the SA node?
Definition
Cardiocytes have a stable resting potential
Term
Stimulus open what type of gates in cardiocytes?
Definition
Voltage-regulated sodium gates - Na+ inflow - depolarisation of cell to threshold
Term
Cardiocytes contract as long as the ion potential is in what?
Definition
Its plateau
Term
Is the plateau in potential more pronounced in ventricular or atrial cardiocytes?
Definition
Ventricular
Term
What happens at the end of the plateau of the membrane potential of cardiocytes?
Definition
Ca2+ channels close and K+ channels open
K+ diffuses rapidly - Ca2+ back into ECF - membrane voltage drops rapidly muscle tension declines
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